1. Field of the Invention
The present invention relates generally to a camera lens assembly, and in particular, to an optical image stabilizer for a camera lens assembly, which corrects an image blurred by shaking of a user's hand (hereinafter, “hand-shaking”) while an object is photographed using a digital camera or an optical device mounted in a mobile communication terminal.
2. Description of the Related Art
With the miniaturization of digital cameras and development of lightweight techniques, the use of mobile communication terminals having optical lenses and camera devices has increased. As the mobility of a camera lens assembly mounted in a mobile communication terminal increases, image blurring caused by fine vibrations or handshaking represents a serious impediment to high quality images. Moreover, frequent photographing during movement increases a need to correct for movement or vibration such as hand-shaking. Although high-resolution cameras have emerged with the development of optical technology, their effect is reduced due to image blurring caused by vibration, so that a need for an image stabilizer increases. Image stabilizing techniques can be roughly classified into two types.
A first type of image stabilization is an electronic image stabilization technique, that is, Digital Image Stabilization (DIS), and Electronic Image Stabilization (EIS), in which blurring is detected from a captured image to correct data stored in a camera device or a memory. The camera device receives a blurred image and generates a clear image by adjusting a position and a color electronically or using a program. The electronic image stabilization technique does not require high cost because separate mechanical and physical configurations are not required, and further because the technique is easily adopted due to few structural constraints. However, adjustment using a program requires a separate memory or a high-performance camera device. A photographing speed may decrease as time required for correcting of a blurred image increases. The extent to which an afterimage is removed using a program is limited, resulting in degradation of a correction rate.
A second type of image stabilization is referred to as Optical Image Stabilization (OIS). An optical image stabilizer detects a user's movements or hand-shaking and changes the position of an optical lens or a camera device. Therefore, blurring of the image formed in the camera device from vibrating is prevented, even during vibration of a photographing device. In the optical image stabilizer, installation of a separate correction device increases a manufacturing cost and requires additional installation space. However, the optical image stabilizer may project a clear image on a camera device and remove an afterimage, thereby maintaining a correction rate of 90% or more. When camera devices having the same performance are used, the camera device using the optical image stabilizer may capture a clearer image than camera devices using electronic image stabilizers. For these reasons, an optical image stabilizer is more widely used than an electronic image stabilizer in photographing devices with high-resolution requirements.
A correction technique using movement of an optical lens may be used in a digital camera or device having a space that is sufficiently large to have a driving unit for driving the optical lens. However, there is a limit in using the correction technique for small digital cameras or mobile communication terminals having space constraints. To solve the problem, a technique for correcting for vibration by moving a camera device has been actively studied. Japanese Patent Application Publication No. 10-39350 discloses an optical hand-shaking correction device. In the disclosed hand-shaking correction device, an X-axis piezoelectric element and a Y-axis piezoelectric element are arranged on the contour of an optical lens and a separate support is provided to support the X-axis and Y-axis piezoelectric elements, thereby causing the optical lens to contact with the driving axis of the X-axis or Y-axis piezoelectric element according to the extent of blurring of a captured image and moving the optical lens by a predetermined distance using frictional force. As such, to install a driving device such as a piezoelectric element on the contour of the optical lens, the outer diameter of the optical lens must be sufficiently large. As a result, the hand-shaking correction device is difficult to mount on a mobile communication terminal, where the length and outer diameter of a camera lens assembly are extremely limited.
Moreover, a difficulty in designing a small-size driving device and a raise in the manufacturing cost caused by an increase in the number of parts impede the cost competitiveness of a photographing device having the hand-shaking correction device embedded therein. In a contact driving device such as a piezoelectric element using frictional force with its driving axis, it is difficult to control the tolerance of a contact face and secure reliability due to malfunction resulting from abrasion of the contact face. A driving circuit for generating and applying a specific voltage waveform is required to drive the driving device such as a piezoelectric element, thus further increasing the manufacturing cost and imposing a limitation on the miniaturization of a photographing device.
Accordingly, a need exists for an optical image stabilizer for a camera lens assembly, which can miniaturize a camera lens assembly to be mounted in a portable electronic device such as a portable terminal and solve a resolution degradation problem due to hand-shaking.